The present invention relates to the use of foamable compositions for packaging purposes. In a number of packaging applications, fragile articles or those otherwise needing protection from undesired movement or breakage, particularly items with irregular shapes and sizes, have been packed in loose, friable or dunnage-type materials or in protective foamed polymer packaging materials, such as injection molded styrofoam, styrofoam chips, or other similar materials.
The present invention relates to foam-in-place packaging, a technique that provides a useful alternative for packaging fragile or other items.
As its name implies, foam-in-place packaging comprises generating the foam cushioning while the articles to be protected are being packaged. For example, when certain chemicals are mixed, they form polymeric products while at the same time generating gases, such as carbon dioxide and water vapor. If such chemicals are selected as being those that harden relatively quickly, they can be used to form hardened polymer foams in which the foam is produced by the gaseous carbon dioxide and water vapor leaving the mixture as it hardens. Typical foamable compositions include urethane precursors which, when mixed, generate polyurethane, carbon dioxide, and water vapor. As the urethane forms and hardens, these gases are concurrently generated so that by the time the urethane sets (generally a relatively short period of a few minutes or less) it takes the form of a polymer foam that has expanded to fill the void spaces in the container and to thereby cushion the item being packaged.
One technique for foam-in-place packaging is to place the object to be packaged in a container, cover it with a polymer film or other material which will protect it from liquids, inject a certain amount of foamable composition into the remainder of the container, and then close the container. As the composition foams, it fills the remainder of the container, forming a custom-shaped foam cushion surrounding the article. Another foam-in-place packaging technique is to form discrete flexible bags and inject a foamable composition into the bags and seal them, whereupon one or more bags are placed into the carton while the foam-forming reaction is taking place and the bags are subsequently expanded by the expanding foam to fill the void space in the carton, the foam then hardening to form custom-shaped cushions protecting the packaged article. In either technique, foam-in-place packaging can be accomplished with a supply of foamable chemicals, usually two, and an injection dispenser connected to the supplies of the respective chemicals. The chemicals are mixed within the dispenser to form the foamable composition. Examples of earlier versions of such dispenser include those described in U.S. Pat. Nos. 3,687,370; 3,945,569; 4,023,733; 4,159,079; and 4,426,023. These patents describe dispensers in which a reciprocally mounted valving rod is movable within a bore into which the foam precursor fluids are introduced through orifices, the bore defining a mixing chamber where the precursor fluids are mixed. The mixed fluids are dispensed out a dispensing opening at one end of the bore when the valving rod is retracted sufficiently to uncover the orifices supplying the fluids to the mixing chamber.
One of the design challenges in making a dispenser for foamable compositions is preventing unwanted accumulation of foam deposits on components of the dispenser, which deposits can build up to the point of rendering the dispenser unreliable or completely nonfunctional. For example, in the dispenser of the type described in the aforementioned patents, a portion of the valving rod is exposed to the precursor fluids, and the inner surfaces of the mixing chamber and other component surfaces are contacted by the exiting foamable composition. Although the valving rod, upon being extended to close the orifices at the end of a dispensing cycle, will to some extent wipe the inner surfaces of the mixing chamber and a portion of the outer surface of the valving rod which moves through the mixing chamber, this cleaning action is in general insufficient to prevent foam chemical deposits from accumulating on the valving rod, which eventually build up and impair the movement of the rod. Moreover, the end or tip of the valving rod is an area that is especially susceptible to accumulations of foam deposits because the wiping action caused by movement of the valving rod is ineffective in cleaning foam deposits from the tip. Furthermore, foam deposits may accumulate in the orifices, another area which is not cleaned by the wiping action of the valving rod.
Prior attempts to deal with the problem of foam deposit fouling of dispensers have focused on designing the dispensers to be readily disassembled to allow the fouled components to be cleaned and reused, and/or designing the dispensers to allow solvents to be introduced into the dispensers to help prevent formation of foam on the components. For example, some dispensers have used solvent chambers which bathe the valving rod in solvent, so that at least a portion of the valving rod which is exposed to the foamable composition is retracted into the solvent chamber during a dispense cycle and exposed to solvent. However, the time required to disassemble a dispenser in order to perform maintenance represents costs in terms of lost productivity and labor cost. Furthermore, although solvent chambers are somewhat effective in helping slow the build-up of deposits on the valving rod, solvent chambers alone are not fully satisfactory solutions to the problem.
Yet another problem with prior dispensers is the tendency of the interference fit between the valving rod and the mixing chamber, which is needed to assure complete stoppage of flow into the mixing chamber when a dispense cycle has been completed, to be degraded through use. Loss of the interference fit results in loss of the ability of the valving rod to effectively seal the orifices into the mixing chamber when the dispensing valve is closed, thus causing leakage of the precursor fluids into the mixing chamber and fouling thereof. The valve body which forms the mixing chamber is typically constructed of a self-lubricating material such as tetrafluoroethylene (TFE) or polytetrafluoroethylene (PTFE). Because these materials have a tendency to cold flow, the repeated sliding of the valving rod into and out of the mixing chamber causes cold working of the valve body, thus causing the degradation in fit between the mixing chamber and the valving rod. Prior attempts to solve the problem have concentrated on applying a restraining force on the valve body via a plurality of stacked Belleville washers which are axially compressed against the valve body to help prevent the cold working of the material. However, Belleville washers have a limited range of movement over which they can maintain a resiliency, and accordingly, the washers have a tendency to lose their restoring force if they are over-extended during installation or use.
Another issue associated with dispensers is that there are advantages in forming a dispenser in modular form such that the components which are most likely to fail or need maintenance or replacement are placed in one module and the more durable components are placed in another module, so that the amount of disassembly required for maintenance and repair can be limited to as great an extent as possible. Specifically, in the case of dispensers of foamable compositions, there are advantages in placing the mixing chamber in one module and the fluid flow control components such as on-off valves in another module. For example, U.S. Pat. No. 4,469,251 describes a hand-held dispenser gun having a detachable mixing chamber. The dispenser includes a control assembly with valves for supplying or interrupting supply of the precursor fluids to the mixing chamber, a head section of the control assembly having two fluid passages for the two precursor fluids. The mixing chamber is removably mounted to the head section by a threaded rod mounted on the mixing chamber and extending through a threaded hole in a rotatable knob secured to the head section, the mixing chamber having apertures into the bore of the mixing chamber which align with the fluid passages in the head section and are sealed thereto by O-rings.
One of the challenges in making such a modular dispenser is preventing leakage at the junctures between the fluid passages of one module and the adjoining fluid passages of another module as fluid is passed through the one module and into the other. Where compressible seals are used for sealing, there is a need to assure a continuous compression force between the modules which will not be lost during use.